Regarding communication system, the basis for accurate information analysis is that the receiver obtains the timing information of received signals. In a mobile communication system in FDD, both uplink and downlink can be asynchronous. The base station and the user employ path searching and tracking in order to obtain timing information of the signals sent out by the other side, especially the timing information of the first path of received signals. Concerning the channel characteristics of a mobile communication system, the location of the first path of received signals will not change significantly within a short time period, however, the signal strength of the path itself is very likely to change greatly within a short time period, therefore, the path searching and tracking employ a method of performing long-term weighted average for signal energy and then using the resultant information for processing. On the other hand, the searching window of the path can be very large in a FDD mobile communication system. For example, the length of searching window of a path in a WCDMA system can be of more than 96 chips, thereby, the estimation error within a short time period will not greatly affect the subsequent performances of the system.
CDMA systems based on TDD all employ special pilot code structure. Its constructing method is to make the channel estimation values with different Midamble (the training sequence portion in the time slot burst structure) shifts in the same time slot be located in different windows for the same channel estimation result, moreover, the window width is comparable to the largest time delay of the path. For example, the length of common channel estimation window in TD-SCDMA system is of 16 chips, while the largest delay of path that can be of more than 15.3 chips. This requires that the received signals of any side in the system possess the characteristics of synchronization or quasi-synchronization, and in particular, the base station must know the starting location of user equipment (UE) transmission signals and track it, and inform UE to perform timing adjustment to achieve the goal of synchronization or quasi-synchronization.
In a TDD mobile communication system, the downlink signal is transmitted synchronously, therefore as for the UE, it can use physical channel (e.g. DwPCH and P-CCPCH) that always possesses signal transmission to perform synchronous searching and tracking; however, in the uplink direction, in order to meet the goal of synchronization or quasi-synchronization, the system needs to execute two steps of initial synchronization establishment and synchronization control, wherein, the former one is the basis for the latter and it is also the premise for realizing the system function.
Regarding to the synchronous TD-SCDMA system and quasi-synchronous TD-CDMA system of the uplink, the synchronization process has a slight difference for uplink initial signals, but every base station chooses the receiving timing of uplink initial signals as the basis for processing. However, the channel delay expanding characteristics causes an inherent error of the base station in determining the initial signal timing, and thereby affects the realization of the system function.
Taking the TD-SCDMA system whose sub-frame is shown in FIG. 1 as an example, a Chinese patent titled as “A building and maintaining method of SCDMA communication link” with patent application number of 97118934.X discloses an establishment method of uplink synchronization, as shown in FIG. 2, wherein it comprises following steps: step 21, UE estimates the distance between itself and the base station; step 22, UE determines the transmission timing based on the estimated distance; step 23, UE transmits signals; step 24, the base station obtains the location of the first path of the received signals; step 25, the network instructs UE to adjust the transmission timing; step 26, UE adjusts transmission timing.
According to this method, the base station can use the tail path of the received UpPTS (uplink pilot time slot) as the initial timing for receiving UpPTS, leading to the misreading of user timing information, which will significantly have an impact on the users under channel conditions with a large time delay expansion, and will even lead to the result that the users can not complete the accessing process. Therefore, improving the uplink synchronization establishment process of TDD mobile communication system that includes TD-SCDMA and TD-CDMA will greatly motivate the development and maturity of related systems.
Meanwhile, the application of joint detection technology has already been proved in both theory and practice. Professor P. W. Baier of Kaiserslautern University in Germany further comes up with the idea of joint transmission technology corresponding to the joint detection technology. This new technology works as follows: in TDD system, when the time interval between the uplink and downlink transmission time slots is smaller than the channel correlated time, the impulse response of the uplink channel and the impulse response of the downlink channel have great correlation, and by using the above characteristics, said technology combines the channel impulse response obtained by uplink joint channel estimation and the user spread spectrum sequence information to pre-process the transmission signals on the side of base station, there is no need to perform channel estimation at the mobile station receiving end, but only to perform related calculations to detect the transmitted signal. Hence, the request for UE joint detection can be converted to the request for base station joint transmission, and complexity of the mobile station is greatly reduced. China patent “A joint optimization signal method based on joint detection and transmission technology” with application number of 03137628.2 makes use of the above technology as the basis. However, there is no realization solution of using joint transmission technology on UE so far.